io THE STRUCTURE AND LIFE OF BIRDS cHap. 
strain is put upon them. The Radius is a very 
slender bone, the Ulna much thicker, with small but 
well-marked projections at the points where the great 
feathers grow. Of the nearer row of carpal bones 
there are only two (RC and UC), whereas there are 
three found in the lizard ; in the bird the small inter- 
mediate one has disappeared, and also the central bone 
Fic. 4.—Hand of (2) Hatteria Lizard ; (2) Chick. 
Cr, near row of carpals; C2, farther row of carpals; cE, central bones—there 
are oftentwo; D 1,2, 3, 4,5, digits; mc, metacarpals; P, pisiform bone, originally a 
tendon; R, radius; vu, ulna. ‘ 
beyond it. Of the more distant row there is not a 
sign in the mature bird, but, if we examine the skeleton 
of an embryo, it may be made out. In a young chick 
there are still two free bones to represent it (C 2, fig. 4). 
In the adult these have been fused with the Meta- 
carpals beyond. The tendency to fusion, or, as it is 
technically called, ankylosis, is found in many parts of 
